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Tuesday, 24 January 2012

How to make a (really) simple DIY solar USB charger for your phone or mp3 player

I am going on a trip in next few days where I will be without power, hence I decided to do some solar charging for my phone. Here is one rudimentary circuit you can make easily.

Parts you need :

Solar cells

Schottky diode 1N5819

Electrolytic capacitor 10uF

0.1uF capacitor

9V rechargeable battery

USB female port

Perfboad or donut board or PCB

Soldering accessories

In this circuit , I use four 5V solar cells. Two are in parallel and other two in series, so that the total output would be 10V and 100mA. I used it because it is the best alternative I have locally. You might choose better alternative like this one. Schottky diode prevents the back current to solar cells. Otherwise, solar cell will draw the current in the dark.

The rest is ordinary LM7805 circuit. This IC will regulate any voltage between 7.5V and 30V to 5V. Capacitor C1 at the input prevents source oscillation while capacitor C2 maintains the output stable.
9V rechargeable battery will act as buffer power source when solar cells are not working.

The simple charging devices (like many phones and mp3, mp4) only use two port of USB ; pin 1 for power and pin 4 for ground. This circuit cannot charge the iPhones , iPods because these devices use other two at specific voltage levels to be able to recognise as charger. See detail explanation about it at Ladyada.net Minty Boost USB charger. It is also not working with my ASUS transformer tablet. But my Nexus S phone is successfully charging.

This is very simple and inefficient design. I have some improved designs in mind. I wanted to use the more efficient step up transformer as in Minty Boost circuit. I am also thinking about using transistors to amplify current. but the problem is I can't buy components I need because of Chinese New Year holidays here. And I really need to finish this solar charger before my trip. Can't really blame it, isn't it engineering is all about ? , to create something with limited resources we have (whether it is time or material).

When my trip is over , I will be improving this circuit once again. Here are photos of my solar charger.

One of my 2012 wish list is to restart blogging. So here it is. I will be talking about some DIY projects of mine as well as my opinions on engineering and technological news that I find interesting. My interest is in consumerization and personalization of medical instruments and treatments which I believe is the next step in reducing the cost and democratizing healthcare for the masses. This blog will also be advocating liberty and freedom in my country and around the world.